The present invention relates to a process for the production of polyethylene compositions. More particularly, it is concerned with a process for efficiently producing polyethylene compositions with filler uniformly dispersed therein by the use, as a catalyst component, of a product resulting from contact treatment of a specific high activity catalyst component with the filler.
Polyethylene is widely used because of its superior properties. In order to improve the properties of polyethylene more so that is can find other new uses, various fillers have been compounded. This compounding is usually carried out by mechanically kneading filler and polyethylene to thereby produce the desired resin composition. This mechanical kneading, however, have various disadvantages. For example, a large amount of kneading energy is needed in uniformly dispersing the filler in the resin, and the filler and resin are deteriorated during the process of kneading. Difficulties are encountered in compounding a large amount of the filler, or in compounding the filler to high molecular weight resins. Since dust is formed during the process, the operation enviroment becomes worse. Moreover, when a filler of high hardness is kneaded, a kneader is seriously worn out.
A compounding technique is also known in which filler is compounded during polymerization of ethylene. In accordance with this method, better dispersion can be attained than that by the above mechanical kneading method. The method, however, suffers from disadvantages in that some more kneading is needed to ensure uniform dispersion and the separation of the filler from the ultimate composition is liable to occur. A process for polymerizing ethylene is also known in which filler treated with the polymerization catalyst comprising an alkyl-aluminum compound and a transition metal compound is employed (see Japanese Patent Publication Nos. 10088/1962 and 11539/1962, and U.S. Pat. No. 3,950,303). The catalyst employed in the above process has, however, low activity. Therefore, in order to reduce halogen compounds contained in the polyethylene composition produced, it is necessary to carry out a deashing step, i.e., a step for removing the catalyst used, or to employ a catalyst containing no halogen compounds.
Accordingly, the process has disadvantages that the preparation of the catalyst and the post-treatment of the polyethylene composition are very complicated. In particular, these disadvantages become serious when the molecular weight of the polyethylene to be produced is lowered by introducing hydrogen gas in order to enhance the fluidity of the polyethylene. This is because the activity of the catalyst is extremely lowered by introducing hydrogen gas.